Question about Effect send/return/insert

Hello, i have this small 7 Channel mixer für my dawless synth setup. I use the Aux send to send channels i want to my sampler. Now i want to send effects to my Korg kaoss nts3 and return it back.

The 'Effects' outputs Mono signal (tested mith stereo Headphones - only left channel had sound). Also the internal effects dissapear when i plug something in 'Effect'. Where can i return the signal back to the mixer? Is it possible that the 'Effect' is a 'insert' so i need Y-splitter? The nts3 has stereo-chinch inputs so that would be not very smart.

Am i thinking false? I thougt mith effect send i could set the amount for the effect going troug with the knobs per channel.